1. Field of the Invention.
The present invention relates to a composition for forming an interpenetrating polymer network and, in particular, wherein such interpenetrating polymeric network is used as a coating.
2. Description of the Prior Art.
A primary concern in the field of coating technology has been the production of a material combining the properties of flexibility, adhesion, hardness, corrosion resistance, humidity resistance and resistance to chemical attack.
In recent years, a further concern in the field of coating technology has been the reduction of the level of volatile solvents emitted during cure. Solvents are used to dilute the coating composition and to facilitate application of the coating composition to appropriate substrates and are released into the atmosphere during cure. To reduce the emission of volatile solvents, such as toluene, methyl ethyl ketone and similar hazardous chemicals has been a longstanding goal of the government on the federal and state level.
Some of the prior art coating compositions include crosslinked polymer networks of chemicals such as epoxy, acrylic, polyester or urethane crosslinked resins. Copolymers formed by chemically crosslinking different polymers to each other have also been formulated in an attempt to obtain satisfactory coating compositions. However, it has been difficult to synthesize copolymers that actually combine the desirable properties possessed by the individual polymer networks crosslinked separately.
Interpenetrating polymer network technology was developed in academic research laboratories. Interpenetrating polymer networks are formed when polymerizable compositions are independently reacted to form distinct, intertwining, continuous polymeric chains. Combining chemically different types of polymeric networks results in the formation of resins having different properties. The interpenetrating polymer network produced exhibits properties that are different from the individual constituent polymers.
The Skinner et al U.S. Pat. Nos. 4,128,600; 4,247,578and 4,342,793 disclose interpenetrating polymer network technology for plastics based on a two-component urethane system polymerized simultaneously with an acrylic monomer. Initially, a polyol and a polyisocyanate are combined with a reactive diluent (the acrylic monomer) having a radiation-sensitive double bond. The polyol and polyisocyanate react to form a crosslinked polyurethane and the reactive diluent is polymerized in a free radical chain reaction separately from the urethane polymerization.